Abstract: This paper aims to investigate the horizontal longitudinal correlation of the near-seafloor sound field in the deep-ocean direct arrival zone (DAZ) and its influencing factors. Through theoretical analysis, numerical simulations, and experimental verification, the variation patterns of the horizontal longitudinal correlation with source frequency, source depth, and receiving range within the DAZ are summarized, along with the high-correlation characteristics at the edge of the DAZ. The relevant research findings indicate that the horizontal-longitudinal correlation characteristics of the near-seafloor acoustic field in the deep-ocean direct arrival zone are primarily governed by the arrival structure and energy distribution of both direct sound and surface-reflected sound. In this region, the horizontal-longitudinal correlation radius of the acoustic field decreases with increasing source frequency and depth, while exhibiting a non-monotonic relationship with reception distance: it first decreases to a minimum at a distance equivalent to \sqrt2/2 times the water depth, then increases. The correlation coefficient oscillates with longitudinal separation, and the oscillation period is modulated by the source frequency, depth, and reception distance. These variation patterns fundamentally align with those observed for the correlation radius. At the edge of the DAZ, the acoustic field is dominated by direct ray bundles exhibiting caustic characteristics, resulting in high correlation.